A simple and highly sensitive electrochemical DNA sensor for the rapid detection of a specific DNA sequence related to the p53 gene is described. The structure and morphology of the synthesized graphene nanosheets and Au nanoparticles were characterized through transmission electron microscopy, UV–Vis spectroscopyand energy dispersion X-ray spectroscopy techniques. The new electrochemical biosensor was prepared by modifying a graphite screen printed electrode (SPE) with gold nanoparticles decorated on graphene (AuNPs/G) nanocomposite. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniqueswere employed to clarify the changes in charge transfer during the fabrication and utilization of the DNA biosensor. The DNA hybridization event was monitored by differential pulse voltammetry (DPV). Under optimal conditions, the decrease of the peak current had a linear relation with the logarithm of the concentration of target complementary DNA in the range 0.5 fM to 0.05 nM, with a detection limit of 0.36 ± 0.04 fM.